Semiconductor display devices such as liquid crystal display devices and EL display devices preferably include semiconductors having the same polarity rather than complementary metal oxide semiconductors (CMOSs) in order to reduce the cost of backplanes (circuit boards). Patent Documents 1 and 2 disclose techniques for forming a variety of circuits such as inverters and shift registers that are used in driver circuits of semiconductor display devices and are constituted of transistors having the same polarity.